The present invention relates to a filtration device for filtering and removing airborne contaminants, such as airborne asbestos fibers. During the process of removing asbestos material from a building, the work area in which the asbestos is contained is subject to substantial airborne asbestos contaminants that are hazardous not only to the workers involved in the asbestos removal process, but hazardous to the outside environment if allowed to escape from the work area. As described in U.S. Pat. No. 4,604,111, a system and method for removing asbestos is known which minimizes the airborne contamination within the work area and prevents the escape of contaminated air outside of the work area in which the asbestos is removed. This system and method, known as the negative pressure method, provides for defining a work area that is substantially sealed but having an opening in the work area so that relatively large volumes of air can be drawn into the work area by a filtration device, which device filters the air and then exhausts the cleansed air outside of the work area. The filtration device, as described in the above-mentioned patent, must be capable of drawing relatively high volumes of air into the work area, thus creating a negative pressure in the work area to prevent any airborne asbestos fibers from leaking outside of the work area. By drawing relatively large volumes of air into the work area, the work area is substantially "cleansed" thus minimizing the airborne asbestos fibers within the work area to prevent contamination to the workers. The filtration device, as described in the above patent, includes a housing having a blower for drawing air into the housing through an air inlet, and filtering the air through filters located within the housing. After the air is filtered, the air is expelled outwardly from the housing, preferably through a hose arrangement that is associated with a wall of the enclosed work area to allow the cleansed air to exit the work area. Various types of filters are used with such filtration device, particularly a HEPA type filter which maximizes the removal of the airborne asbestos fibers.
Prior art filtration devices used in connection with asbestos removal procedures are known in the art. In addition to the filtration device as described in U.S. Pat. No. 4,604,111, filtration devices, or units, have been manufactured and sold by Micro-Trap, Inc., as well as other entities. The Micro-Trap filter units include a housing having an inlet for receiving contaminated air and an outlet for expelling the filtered air to the exterior of the housing. A filter, including a HEPA filter, is installed in the housing in sealed communication across the air inlet. Downstream of the HEPA filter is a blower for drawing air through the filter and for expelling the filtered air through the air outlet to the outside of the housing.
Such units include a display and alarm panel for providing basic control and display functions. For example, such units may include an analog pressure gauge for providing a visual read-out of the differential pressure between the housing interior, downstream of the filter, and the exterior of the housing. Such pressure gauge includes two air inlets, one of which is in communication with the interior of the housing and the other of which is in communication with the exterior of the housing for receiving the atmospheric air. This differential air pressure is displayed on the pressure gauge located at a suitable control panel mounted on the side of the housing. The pressure gauge indicates this differential pressure, in inches of water (WG).
In addition, such units may include pressure switches which are pre-set to predetermined high and low pressure values. When the high and low pressure limits are exceeded, visual and audible indications are provided on the control panel. Still further, the units include a shut down timer that will enable the operator to set the blower motor to operate for a pre-set time period. An elapsed time meter is also provided to display the total operating time of the unit. Further, certain of such prior art units include a blower motor speed control knob to control the motor speed of the blower motor. None of the control/display features of such prior art systems are microprocessor controlled.
In order to optimize the effectiveness of filtration units in connection with asbestos removal within a substantially enclosed work area, the operating personnel need to be aware of, and be able to control, the air flow through the enclosed work area to assure optimum filtration and removal of the airborne asbestos contaminants. It is desirable that the operator of the filtration unit have a visual readout of the air flow rate through the filtration unit, in cubic feet per minute (CFM) and to provide for some means to alter or adjust the air flow rate depending upon the particular air flow requirements. Further, during the usage of any filtration unit, as the unit is used, the filters get clogged, thus altering the air flow rate through the system. Among the disadvantages of the above systems is the inability to provide a visual indication of the air flow rate in cubic feet per minute during system operation and to provide for some mechanism for automatically ensuring a stable air flow rate under all system conditions, i.e., as the filter becomes clogged with contaminants. Moreover, such units lack the ability to monitor various electrical characteristics, such as the incoming line voltage. Still further, such units do not lend themselves to remote monitoring and control, thus necessitating personnel having to enter the contaminated area to monitor or alter the operation of the units.